Prior heat exchangers have had various features. Thus, U.S. Pat. No. 1,789,733 discloses a heat exchanger for cooling water in which a series of four coils spiral upwardly in a spaced, rectangular configuration from a lower header to an upper header, while brine or other liquid is fed into a tank in which the coils are installed through nozzles located on a central standpipe. The refrigerant is introduced into the lower header in liquid form and forms a gas during upward passage in the coils. U.S. Pat. No. 2,241,186 discloses a liquid cooler including a tank for a fluid refrigerant, such as freon, ammonia, carbon dioxide, etc., and coils inside the tank formed from tubes of increasing diameter, joined end to end, in three sets. The smallest tubes are each wound in three interposed coils, each forming a pair of concentric inner coils spiralling in opposite directions and connected at one end. A set of three interposed, concentric pairs of intermediate coils are connected at one end to the outer of the corresponding smaller coils and at the opposite end of each other, while three interposed outer coils are of still larger size, are connected to the outermost intermediate coils and spiral in the opposite direction. The purpose of the increase in the size of the coils is to prevent a liquid, such as water, from freezing while being cooled to below its freezing point. The flow of water is in both directions with respect to the horizontal, longitudinal axis of the tank, while the flow of refrigerant is essentially vaporization in the lower portion of the tank and withdrawal of vapor at the top. Also, the coils are spaced apart by longitudinal rods. U.S. Pat. No. 2,530,519 discloses a cooker in which a pair of concentric coils, one within the other but separated by circumferentially spaced rods, extend upwardly from a common lower header to a common upper header. U.S. Pat. No. 3,639,963 discloses a method of making a heat exchanger and coil assembly in which the coil turns are arranged in concentric layers, are spaced apart by spacer members and are secured together by dip soldering. The coils are formed from one continuous tube which alternates in going from an inner coil to the outer coil at the top and bottom, respectively. U.S. Pat. No. 3,738,842 discloses a heat exchanger for cooling water in which a refrigerant tubing is flattened against the exterior of a tank to form a spiral coil and a water tube extends spirally around the outside of the flattened refrigerant tube, then connects with the inside of the tank at the bottom. U.S. Pat. No. 3,921,708 discloses a heat exchanger having a single coil spiralling about a central tube, with a spiral ribbon interspaced between turns. The wall of the tube is corrugated to permit expansion and contraction. U.S. Pat. No. 4,036,621 discloses a beverage dispenser in which concentric coils are located in spaced arrangement inside a tank, i.e. one inner coil and two spaced apart outer coils. Also, heat conducting rods extend axially from the inside to the outside of the turns of the inner coil. U.S. Pat. No. 4,061,184 discloses a heat exchanger for a refrigerated water cooler in which a refrigerant circulating coil is wound about the outside of a tank, while the water to be cooled is fed into the upper portion of the tank. A cylinder having an open top and a closed bottom, except for a relief valve, is spaced inwardly from the tank side wall, while a coil extends spirally in the space between the cylinder and the tank. This coil has an open bottom turn but an inlet spaced above the water inlet, for overflow into the inlet and movement of water down the coil when the water reaches such an upper level.
None of the above heat exchangers provide the distinguishing features or combination of features of the heat exchangers of the present invention.